Projectile weapon aiming systems are discussed herein principally with reference to their use on rifles and embodied in telescopic sights commonly known as riflescopes. It will become apparent, however, that projectile weapon aiming systems may include aiming devices other than riflescopes, and may be used on weapons other than rifles, which are capable of propelling projectiles along substantially predeterminable trajectories, e.g., handguns, crossbows, and artillery.
A factor that must be taken into account in long-range shooting is the curved trajectory traversed by a bullet or other projectile as it falls from its initial trajectory while traveling the distance from the gun to the target, i.e., “range.” An aiming line of sight emanating from a reticle aiming mark of a riflescope rigidly affixed to the gun is straight, and hence the line of sight can intersect the curved trajectory only at a discrete range. At other ranges the projectile will pass below or above the aiming line of sight, necessitating the use of elevation adjustments for aiming. Elevation adjustments in such riflescopes are typically made by turning an adjustment mechanism of the riflescope to impart vertical movement of optical elements (as described, for example, in U.S. Pat. No. 3,297,389 of Gibson) or of the reticle (as described, for example, in U.S. Pat. No. 3,058,391 of Leupold), so that the aiming line of sight is accurately “sighted-in” at the range of the target. To adjust for the effect of crosswinds, riflescopes also typically include a separate adjustment mechanism for imparting horizontal movement to the optical elements or reticle. In yet other projectile weapon aiming systems, the entire aiming device is adjusted relative to the weapon via an adjustable sight mount. Adjustment of the elevation and windage is time consuming and may require the shooter to take his or her eyes off the target while manipulating the adjustment mechanisms.
There have been proposed numerous reticles and riflescopes designed to provide the shooter with a plurality of aiming marks for shooting at targets at various predetermined ranges, i.e., aiming marks producing line of sight/trajectory intersections at various ranges. Some of these include devices for approximating the range to the target. These riflescopes propose to eliminate the need to make elevation adjustments in the riflescope to compensate for bullet drop at different ranges. Exemplary riflescopes are disclosed in U.S. Pat. Nos. 3,190,003 of O'Brien; 1,190,121 of Critchett; 3,392,450 of Herter et al.; 3,431,652 of Leatherwood; 3,492,733 of Leatherwood; 6,032,374 of Sammut; and 6,591,537 of Smith. Most of these patents propose riflescopes providing a plurality of range-related aiming marks accompanied with aiming mark selection devices, the use of which depends on relative height of the image of a target of known or estimable height compared to the height of a feature in the reticle.
Using modern laser rangefinders and other ranging techniques, it is now possible to quickly determine a range to target more accurately than by using one of the range-finding reticles described above.
U.S. Pat. No. 3,948,587 of Rubbert proposes a riflescope with a reticle that includes vertically adjacent target-spanning and aiming apertures dimensioned so that when a target of known or estimable size is framed in one of the apertures, the gun is thereby aimed for the correct range to the target. However, Rubbert does not provide an aiming mark or points of reference when the target is at a range such that it does not fit any of the apertures. The apparent spacing of the target-spanning and aiming apertures can be changed by varying the optical power of the riflescope; however, due to a limited amount of optical power adjustment available, the riflescope of Rubbert is useful only for aiming at targets within a limited size range. For example, Rubbert describes a riflescope that can be adjusted for use in aiming at targets sized between 14 and 40 inches in height. Attempting to fit smaller or larger targets in the apertures would result in gross aiming errors.
U.S. Pat. Nos. 6,032,374 of Sammut and 6,591,537 of Smith propose reticles having a series of secondary aiming marks spaced below a primary aiming mark at predetermined intervals for compensating for bullet drop. After determining or estimating an observed range, the shooter selects the secondary aiming mark most closely corresponding to the observed range. The secondary aiming marks of Sammut are evenly spaced, but a bullet's trajectory is parabolic, so Sammut requires preliminary collection of ballistic data to determine the range corresponding to each secondary aiming mark. The corresponding ranges determined by the collection of ballistic data are applicable only for the ballistics of particular ammunition for which data is collected. Furthermore, a shooter must either memorize the ranges that are empirically determined or refer to a worksheet where the ballistic data and corresponding ranges have been recorded.
Smith purports to provide secondary aiming marks for regular incremental ranges (typically 300, 400, 500, and 600 yards) in an attempt to eliminate the need, as with the device of Sammut, to refer to ballistics data or to memorize the ranges corresponding to the secondary aiming marks. However, the ranges of the secondary aiming marks of Smith are accurate only for a particular predetermined rifle and ammunition combination, referred to as the ballistic “factor.” For ammunition having a ballistic factor different from the factor for which the reticle is designed, Smith proposes to apply a decal to the stock of the rifle or some other convenient location for reference in determining the irregular ranges at which the secondary aiming marks can be used to aim the rifle.
The present inventors have recognized a need for an improved projectile weapon aiming system for accurately compensating for ballistic drop and windage for a variety of ammunition having different ballistic characteristics.